BEIRUT, Lebanon — Multiple airstrikes hit a busy market in a rebel-controlled town in northwestern Syria on Monday, killing at least 27 people and turning several buildings into piles of rubble, according to opposition activists and a war monitor.
Shortly after the strikes, state media said rebels shelled a government-held village, killing seven.
The high death toll marked a sharp increase in the escalation of violence between the two sides. Government troops, backed by Russian air cover, have been trying since April to push their way into the enclave in the northwestern corner of Syria, near the Turkish border.
Dominated by Al Qaeda-linked militants and other jihadi groups, Idlib province and northern parts of the nearby Hama region are the last major rebel strongholds in the country not controlled by Syria’s president, Bashar al-Assad.
Despite the heavy bombardment, Mr. Assad’s forces have been unable to make significant advances. Militant groups have hit back hard, killing an average of more than a dozen soldiers and allied militiamen a day in recent weeks.
The fighting has killed more than 2,000 people and displaced hundreds of thousands.
The Syrian military’s struggling campaign underscores the limits of Syria’s and Russia’s air power and inability to achieve a definitive victory in the country’s long-running civil war, now in its ninth year.
Monday’s airstrikes took place in the town of Maaret al-Numan and left more than 30 injured, according to the reports from the region, which has witnessed intensive airstrikes and bombardment almost every day for the last three months. The strikes came in several rounds and caused widespread destruction, burying several people under the rubble.
The Britain-based Syrian Observatory for Human Rights, a war monitor, called it the largest single death toll since a Russian-Turkish truce collapsed in late April.
SANA, the Syrian state news agency, said insurgents shelled the village of Jourin in the northern part of Hama province, killing seven civilians when a shell hit a moving car. State TV also reported that insurgents shelled the government-held town of Suqailabiyah, injuring four people, including a child.
Syrian opposition activists said Russian warplanes carried out Monday’s airstrikes, but Russia’s Defense Ministry dismissed the reports as a “hoax,” adding that the Russian air force didn’t “carry out any missions in that area in Syria.” There was no immediate comment from the Syrian government.
The Observatory, which monitors the fighting on the ground in Syria through a network of activists, said 37 people were killed, including two children and three women, in the strike on Maaret al-Numan. The Thiqa news agency, an activist collective in northern Syria, reported that the strike killed 27 people.